Long Term Evolution (LTE) of 3GPP continues to use a traditional homogeneous network which is constructed by a hexagonal cellular system. In order to further improve system capacity, Advanced LTE (LTE-A) of a next generation wireless communication system introduces a heterogeneous network. The LTE-A system includes a macro cell, a femto cell, a pico cell, a Remote Radio Head (RRH) and a relay. By deploying new wireless nodes, the LTE-A system not only improves the system capacity, but also provides better services to the users of special areas and optimizes the system performance. On the other hand, the newly deployed nodes bring interferences to the users of the originally deployed cells, and an enhanced interference coordination method is required. Coordinated Multi-Point (CoMP) technology uses multiple cells for a joint transmission, thereby suppressing the inter-cell interferences and improving the system performance.
In the heterogeneous network including the macro cell and the RRH, cells may be deployed in two modes. FIG. 1 illustrates a first configuration of the heterogeneous network including a macro base station and the RRH. As illustrated in FIG. 1, a first mode is that the macro cell and the RRH use the same cell identifier (Cell-ID). Under this scenario, the macro cell and the RRH use the same PDCCH, PHICH, PCFICH, PBCH, PSS, SSS, SIB channel and CRS, but the PDSCH channel may be multiplexed in the CoMP transmission mode. This deployment mode has the following advantages: (1) the PDCCH/PHICH/PCFICH/PBCH/PSS/SSS channel can obtain the diversity gain; and (2) there is no inter-CRS interference between the cells. The disadvantage is that the multiplexing gain will be lost in the PDCCH/PBCH/PSS/SSS channel. FIG. 2 illustrates a second configuration of the heterogeneous network including the macro base station and the RRH. As illustrated in FIG. 2, a second mode is that the macro cell and the RRH use different cell identifiers (Cell-IDs). Under this scenario, the macro cell and the RRH multiplex the PDCCH, PDSCH, PHICH, PCFICH, PBCH, PSS, SSS, SIB channel and CRS. This solution has the following advantages: (1) a maximum channel multiplexing gain can be obtained; and (2) a smooth evolution is made in the previous interference coordination mechanism, and a good compatibility is achieved. The disadvantage is that there are strong inter-cell interfaces, and the diversity gain cannot be obtained. FIG. 1 illustrates a schematic diagram of the two scenarios.
Under both cell deployment modes, the PDSCH can obtain the multiplexing gain, but the PDCCH/PHICH/PCFICH/PBCH/PSS/SSS/CRS have different transmission modes. The design objective of the solution of FIG. 1 is to obtain the diversity gain, and the design objective of the solution of FIG. 2 is to obtain the multiplexing gain.
In the studies the inventor finds that the solution of the prior art is not flexible enough, and it can only implement the diversity gain or the multiplexing gain, and the system capacity is limited to be further improved. Therefore, an allocation method relating to the cell identifier is required for a compromise between the diversity gain and the multiplexing gain.
Although the above technical solutions are proposed in the Background section for the convenience of description, it shall not be deemed that they are well known to a person skilled in the art.